1. Field of the Invention
The present invention relates generally to rotating disk technology, particularly to disk drive apparatus employed as a memory device and, more specifically, to a technique for determining computer hard disk alignment and alignment shifts and for providing compensation.
2. Description of the Related Art
In the state of the art of digital data storage, hard disks form the basis for main memory in most computer systems. Hard disk drives provide rapid access to a very large number of data records. Magnetic storage hard disk drives are faster than floppy disk, magnetic tape, and optical disk drives, and cost less than equivalent capacity semiconductor memory. Fundamentals of magnetic recording and disk drives can be found in The Complete Handbook of Magnetic Recording by Finn Jorgensen, copyright 1988 (3rd Edition, TAB BOOK Inc., Blue Ridge Summit, Pa.)
FIG. 1 (Prior Art) illustrates the fundamental components of a computer memory, hard disk apparatus (generally referred to simply as the xe2x80x9chard drivexe2x80x9d), head-disk assembly 101. A stack 103 of individual disks 103a, each having magnetic recording surface layers (on both sides of the disk), rotates (arrow 105) at a constant speed (e.g., approximately 5400 RPM) on a hub 106 suitably mounted on a base plate 108. Mounted in a head stack assembly 111, load beams 107 extend magnetic transducers (xe2x80x9cheadsxe2x80x9d) 109 which are selectively positioned with respect to each disk""s recording surface in order to read and write digital data on the disks 103a (see also FIG. 2). A coil 113 on the head stack assembly 111 interacts with a magnetic drive subassembly 117 to swing the head stack assembly via a rotary shaft, or pivot bearing, 115 reversibly driven about the shaft axis, selectively moving the heads 109 from the inner diameter data tracks to the outer diameter data tracks of the recording surfaces. Appropriate electronics (not shown) are provided for controlling positioning and performing read/write functions via the heads 109. (See also FIG. 2 regarding disk formatting). The head stack assembly 111 in combination with the magnetic drive subassembly 117 and pivot bearing 115 is referred to as the xe2x80x9cactuator assembly. xe2x80x9d In the state of the art, the typical read/write head may have physical dimensions of approximately 0.080-inch by 0.00125-inch; the height of the head above the disk surface may be on the order of approximately 0.75-micro-inch. Because of its shape, the head stack assembly main body part which encompasses the rotary shaft 115 is referred to as an xe2x80x9cE-block.xe2x80x9d A unitary E-block assembly for use in a disk drive is disclosed in U.S. Pat. No. 5,095,396 (Putnam et al., assigned to the common assignee of the present invention.)
FIG. 2 (Prior Art) illustrates the fundamental constructs (dimensions exaggerated) involved in recording data on a magnetic disk 203. Physically, a hard drive disk comprises an aluminum substrate platter having a series of thin film layers thereon used in the data recording process and an outer, protective lubricant layer open to the environment (see e.g., U.S. Pat. No. Re. 32,464 (Aine) and its related patents). The disk 203 is formatted by dividing it into sectors 212 by a number of radially-extending spokes 214 placed at regular angular intervals about the disk. The spokes 214 are areas on the disk containing tracking servo bursts and sector identification information. The sectors 212 are areas on the disk containing data blocks 216, each block having a fixed amount of data, for example 512-bytes. The data blocks 216 occupy circular tracks 218. The tracks 218 are grouped into bands 220; all of the tracks 218 in a given band 220 contain the same number of radially aligned data blocks 216. The section of a band 220 where a set of radially aligned data blocks 16 is recorded is called a block frame 222. The number of block frames 222 per band increases with band 220 radius. The beginning and end of a block frame 222 are defined by a timing system in a disk controller (not shown). The number of bands 220 is maximized if each band has exactly one more block frame 222 than its inwardly adjacent band. In that case, the number of bands 220 is simply the difference between the number of block frames 222 in the outermost band and the number of block frames in the innermost band. The spokes 214 are numbered, e.g., zero to seven, in the direction opposite to disk rotation. The sectors 212 are also numbered, each sector being numbered the same as the immediately preceding spoke 214. The block frames 222 in each band 220 are numbered starting from zero; block frame zero in each band is adjacent to spoke zero. In order to maximize storage capacity of the disk 210, the data blocks 216 along the innermost track 218 of each band 220 are recorded as close as possible to a predetermined maximum linear bit density. As a result, the data rate in megabytes per second in each band increases with radius. The number of tracks 218 is predetermined for a given disk, normally spaced as close as possible to maximize storage density. In the state of the art, typical track density is approximately fifteen thousand (15,000) TPI; a typical data bit density is approximately two-hundred twenty thousand (220,000) BPI; average access time to find any particular data stream is approximately five-to nine milliseconds, holding several gigabytes of information.
The location of any recorded programs and data is stored in a directory area on a disk and informs the disk operating system about the exact sector and track number where the recorded data are to be found. Servo burst signals recorded in the spokes 214 provide positioning information; generally, amplitude and phase of servo-signals provide correction signals to the motor drive electronics associated with the actuator assembly. As known in the art, the design of servo-follower mechanisms, associated electronics, and optimized servo-tracking algorithms requires an analysis of the specific disk drive design implementation. While servo-tracking algorithms can provide for track following where small distortions are involved (e.g., xc2x1100-microinch), inherent limitations in servo-tracking algorithms limits the tracking correction which is available for gross track shifts such as might occur if the head-to-track alignment is skewed, such as by a shock event. With the recognition of the advanced state of the art of such servo technology, a further detailed description is not necessary to an understanding of the present invention for a person skilled in the art.
As should now be recognized, considering the speed of the disk, the size of the heads, the complex data formatting on the disk, servo-follower limitations, and the high track and bit densities, for reliable read/write functionality it is critical that head-to-track alignment be precise.
Disk drive durability has to be maintained under sometimes severe environmental conditions, particularly during computer assembly and in the actual use of portable computers. One of the parameters that affect drive durability is shock, used to describe impact loading of drives. Shock is characterized by its magnitude in G-forces and shock duration. In disk drive technology, withstanding a shock implies that the head-media interface reliability is not compromised due to violent dynamic response of drive components following the shock event. To improve drive insensitivity to both computer assembly process, transportation, in-use handling conditions, and any other environmental situation in which a shock might be imparted to a unit, drive manufacturers are forced to design systems able to withstand higher G-forces over shorter durations; an exemplary shock load specification goal is for a disk drive to withstand a shock of 1000-G""s at 1-millisecond without affecting performance.
One of the primary drive failure modes caused by a shock event is referred to as xe2x80x9cdisk shiftxe2x80x9d or xe2x80x9cdisk slippage.xe2x80x9d As shown in FIGS. 3A and 3B and discussed in more detail elsewhere in this specification, following a shock event, disk shift may have changed the head-to-rack alignment. Due to a gross shift of written tracks of a formatted disk, the head is unable to follow during a read cycle, resulting in data read mode failures. There is a need for a method and apparatus for facilitating the determination of and compensation for disk shifts.
In a basic aspect, the present invention provides a method for profiling alignment of a rotating disk having a given radius. The method includes the steps of: providing a predetermined marker on a periphery of the rotating disk; and starting at the marker, as the disk revolves about its axis of rotation, plotting variations of proximity of the periphery of the disk between the periphery and a predetermined radial position greater than the given radius such that a plot of the variations from the marker over one revolution constitutes an initial alignment profile of the disk to the predetermined radial position. By periodically re-plotting variations of proximity of the periphery of the disk between the periphery and a predetermined radial position greater than the given radius, the re-plot of the variations from the marker over one revolution constitutes a secondary alignment profile of the disk to the predetermined radial position. The comparison of the plot to the re-plot is indicative of a change of alignment of the rotating disk.
In another basic aspect, the present invention is used in a computer memory hard disk drive, having at least one disk having a given radius and a given initial axis of rotation, the drive including at least one transducer, movably mounted for reading data recorded on concentric tracks of the disk. A method for determining disk shift includes the steps of: providing a predetermined edge marker on a periphery of each rotating disk; starting at the edge marker, creating a first plot of variations of proximity of the periphery of the disk to a predetermined radial position greater than the radius as the disk revolves about the given initial axis of rotation; storing the first plot as a first reference data set; periodically, starting at the edge marker, creating a second plot as a second reference data set of variations of proximity of the periphery of the disk to the predetermined radial position greater than the radius as the disk revolves; comparing the first data set with the second data set; and determining disk shift as a function of differences between the first data set and the second data set.
In another basic aspect of the present invention, a computer memory hard disk drive is provided, having at least one disk having a given radius and a given initial axis of rotation, the drive including at least one selectively positionable transducer for reading data recorded on concentric tracks of the disk. A method for determining and compensating for disk shift includes the steps of: starting at a point on an outer diameter of the disk, creating a first data set indicative of variations of proximity of the periphery of the disk to a predetermined radial position greater than the radius as the disk makes a single rotation about the axis; storing the first data set; periodically, starting at the point, creating a second data set of variations of proximity of the periphery of the disk to a predetermined radial position greater than the radius as the disk makes a single rotation; comparing the first data set with the second data set; determining disk shift as a function of differences between the first data set and the second data set; and if the disk shift is a function value greater than a predetermined transducer-to-track alignment tolerance, compensating transducer-to-track following by the function value.
Another basic aspect of the present invention is a hard disk adapted for use as a memory apparatus; the disk includes: a substrate; superjacent the substrate, at least one thin film layer associated with recording digital data in a plurality of tracks thereon; and at least one topographical anomaly located in a peripheral edge of the disk providing a marker such that proximity variations of the peripheral edge to an edge proximity detector can be plotted as a function of angular location with respect to the marker as the disk rotates past the edge proximity detector.
Another basic aspect of the present invention is a disk drive read-write head gimbal assembly mount adapted for positioning at least one read-write transducer with respect to a rotating disk, the head gimbal including: body mechanisms for positioning the read-write transducer with respect to a recording surface of the rotating disk; and mounted on the body mechanisms, detecting mechanisms for measuring proximity variations between the body mechanisms and the recording surface as the disk rotates past the detecting mechanisms.
In another basic aspect, the present invention provides a computer memory disk drive system. The system includes: at least one recording disk having a plurality of concentric data tracks thereon, the disk having an outer diameter edge at a predetermined radius and an axis of rotation; at least one transducer positionable for at least reading information contained on the data tracks; a transducer mount, movably mounted adjacent to the recording disk, for selectively positioning the transducer with respect to concentric tracks on the disk; attached to the mount, at least one proximity detector for alignment of the transducer to the tracks.
In another basic aspect, a predetermined alignment feature is embedded into the recording surfaces of a disk. As is known in the art, a change in spacing between the head and the disk surface can be recognized as magnetic or thermal flux variations. For a magnetic disk, a sequential series of individual surface anomalies that are recognizable by the read head can be scribed or are embedded in the alignment track. Thus, from a start/stop gap of the feature, a series of surface anomalies is scribed along the predetermined alignment track which will induce a pattern of such effects in the read head when in a read-back-mode and aligned to that track as the disk spins. In commercial application, each disk is implanted with the alignment track feature before incorporation into a head-disk assembly. Next, the alignment track is mapped and stored. The drive""s read head is used in a read-back-mode to digitally describe an initial profile, or map, of the alignment track. A digital pattern representation of the initial profile is stored as read-only data in a memory by any known manner or proprietary data processing program. The initial profile is now available for use in various operational modes of the disk drive. When a disk shift test is called for, a current profile of the test track is made and stored using the head in a read-back-mode simply by running the read head about the alignment track, reading the predetermined feature and storing the current profile. The two stored maps, the initial profile and the current profile are compared. If the maps are identical, or within a predetermined tolerance defined for a specific implementation knowing the drive""s particular servo-tracking algorithm limitations, the system standard read-write mode can be initiated. If it is determined that significant track distortion has occurred due to disk shift, the servo-tracking algorithm is modified to conform track following in all future read-write mode operations. The servo-tracking modification is simple as the distortion is a direct function of track angular location to the initial configuration. Thus, the track position compensation value is a constant. The data processing involved in mapping, storing, and comparing alignment track profiles can be implemented in either a firmware and semiconductor memory form or in software as part of a disk drive""s software driver program.
In a further basic aspect, the present invention provides a method for determining a shift of a disk having a plurality of tracks thereon. The method includes the steps of: forming a series of fixed anomalies on a surface of the disk; forming an initial profile of track alignment based on a positional profile of the series of fixed anomalies; storing the initial profile; periodically forming a current profile of the series of fixed anomalies; comparing the initial profile to the current profile; and deriving a measurement of disk shift from detected differences between the initial profile and the current profile.
In a further basic aspect, the present invention provides a method for determining and compensating for disk slippage of a computer memory disk having a plurality of data tracks thereon in a disk drive having a read head adapted for following the data tracks. The method includes the steps of: forming a series of fixed anomalies on a surface of the disk; forming an initial profile of data track alignment from the series of fixed anomalies; periodically forming a current profile of data track alignment from the series of fixed anomalies; comparing the initial profile to the current profile; deriving a measurement of disk shift from detected differences between the initial profile and the current profile; and adjusting data track following in conformance with the measurement of disk shift.
In a further basic aspect, the present invention provides a track alignment pattern for a disk shaped data recording medium having at least one recording surface thereon, the surface adapted for having a plurality of concentric recording tracks thereon, the pattern comprising a sequence of geometric features scribed onto the recording surface of the disk in at least one predetermined track at a substantially constant radial distance from the axis of rotation of the disk, forming a pattern for mapping concentric alignment of the disk with respect to the axis of rotation.
In a further basic aspect, the present invention provides a computer memory disk adapted for use with a read head, the disk including: a substrate; superjacent the substrate, at least one thin film layer associated with recording digital data therein; and a series of anomalies in the thin film layer such that the anomalies are identified by the read head as an alignment feature for the disk.
In a further basic aspect, the present invention provides a disk drive including: at least one recording disk having a plurality of concentric data tracks thereon; at least one transducer for at least reading information contained on the data tracks; at least one of the data tracks being a predetermined track having a set of topographical features embedded thereon such that the transducer is usable as a mechanism for forming an initial profile of the predetermined track having a set of topographical features embedded thereon wherein the initial profile is an initial track alignment map of the plurality of concentric tracks; and mechanisms for selectively forming a current profile of the predetermined track having a set of topographical features embedded thereon and for comparing the current profile to the initial profile and for resetting data track following of the transducer to compensate for differences between the initial profile and the current profile.
It is an advantage of the present invention that it provides a method for accurately determining and compensating for disk shifts.
It is another advantage of the present invention that relatively gross disk slippage can be accommodated with little impact to the read/write performance of the drive.
It is another advantage of the present invention that it can be implemented with no changes to either the heads or the fundamental media design.
It is another advantage of the present invention that it provides a disk drive that can withstand higher shocks without affecting performance.
It is still another advantage of the present invention that it overcomes limitations in servo-tracking algorithms ability to compensate for data track shifts.
It is a further advantage of the present invention that it provides a mechanism for determining shock event disk shift effects without requiring contact with the disks.
It is a further advantage of the present invention that it requires no added hardware to the disk drive construct.